Many different orthopedic casting materials have been developed for use in the immobilization of broken or otherwise injured body limbs. Some of the first casting materials developed for this purpose involve the use of plaster of Paris bandages consisting of a mesh fabric (e.g., cotton gauze) with plaster incorporated into the openings and onto the surface of the mesh fabric.
Plaster of Paris casts, however, have a number of attendant disadvantages, including a low strength-to-weight ratio, resulting in a finished cast which is very heavy and bulky. Furthermore, plaster of Paris casts typically disintegrate in water, thus making it necessary to avoid bathing, showering, or other activities involving contact with water. In addition, plaster of Paris casts are not air permeable, and thus do not allow for the circulation of air beneath the cast which greatly facilitates the evaporation and removal of moisture trapped between cast and skin. This often leads to skin maceration, irritation, or infection. Such disadvantages, as well as others, stimulated research in the orthopedic casting art for casting materials having improved properties over plaster of Paris.
A significant advancement in the art was achieved when polyisocyanate prepolymers were found to be useful in formulating a resin for orthopedic casting materials, as disclosed, for example, in U.S. Pat. No. 4,502,479 (Garwood et al.) and U.S. Pat. No. 4,441,262 (Von Bonin et al.). U.S. Pat. No. 4,502,479 sets forth an orthopedic casting material comprising a knit fabric which is made from a high modulus fiber (e.g., fiberglass) impregnated with a polyisocyanate prepolymer resin such as polyurethane. Orthopedic casting materials made in accordance with U.S. Pat. No. 4,502,479 provide significant advancement over the plaster of Paris orthopedic casts, including a higher strength-to-weight ratio and greater air permeability. U.S. Pat. No. 4,667,661 (Scholz et al.) discloses a casting tape which further comprises a lubricant. The lubricant serves to provide a casting material which is easy to apply and slippery to mold without the resin sticking to the gloved hands of the applier.
Examples of an orthopedic bandage using a polyester fabric which is not a knitted fabric is disclosed in U.S. Pat. No. 3,972,323 (Boricheski) (comprising plaster of Paris binder) and U.S. Pat. No. 4,841,958 (Ersfeld et al.). However, the polyester fabric backing disclosed in U.S. Pat. No. 4,841,958 causes the cast to have a somewhat lower strength and a lower rigidity than fiberglass casts. As such, these casting materials require more layers of casting tape to achieve a weight bearing orthopedic cast.
Several "roll-form" casting tapes have been disclosed which comprise a fabric impregnated with a curable resin. Examples include materials based on free radical acrylate or acrylamide functional resins which may be cured by a redox reaction upon activation by water (see, e.g., U.S. Pat. No. 4,672,956), and two part systems wherein one component is coated on a tape and a separate reactive component is provided in a separate sealed ampoule (see, e.g., U.S. Pat. No. 4,498,467). However, more commercially successful casting tapes generally include materials based on isocyanate functional polyurethane prepolymers. Common to all these roll-form casting tapes, a viscous liquid resin is impregnated into a fibrous backing material such as a knit, woven, or non-woven material. The backings may be comprised of either natural or synthetic fibers or both. In general, the resin is primarily retained (i.e., "held") by the backing by capillary force. However, in order to ensure adequate layer-to-layer lamination in the applied cast it is often necessary to apply more resin than the backing can actually hold. Furthermore, the resin viscosity is often deliberately low to facilitate coating and handling properties such as the ease by which the roll unwinds and the conformability of the material to the patient's limb. Unfortunately, gravitational forces cause resin migration between layers and toward the bottom of the roll. This migration is often referred to as resin "pooling."
A cast material comprising a filled thermoplastic crystalline solid polyurethane is disclosed in U.S. Pat. No. 4,473,671 (Green). In use, the orthopedic cast material is warmed to a sufficiently high temperature to cause the polymer therein to become soft enough to deform. The orthopedic cast material is molded to conform to the surface shape of the effected portion of the body and then is cooled to room temperature. U.S. Pat. No. 4,454,873 (Laufenberg) discloses an orthopedic cast material comprising a thermoplastic material and a coating of (poly)ethylene oxide. The coating is said to prevent adherence of adjacent convolutions of the cast material when it is molten.
A tubular casting system comprising an integral tubular bulky knitted substrate carrying a hardenable resin and an undercast padding layer is disclosed in International Patent Application No. WO 90114060 (Blott et al.). A water soluble but resin impervious barrier layer intermediate to the padding and resin bearing layers is discussed.
From the foregoing, it will be appreciated that what is needed in the art is an orthopedic casting material which has the moldability of plaster of Paris, the high strength-to-weight and good air permeability of non-plaster of Paris materials, and which is non-sticky during application. In this regard it would be a significant advancement in the art to provide such a combination of advantages without actually using plaster of Paris, thereby avoiding the inherent disadvantages of plaster of Paris outlined herein. It would be a further advancement in the art to provide casting materials which resist resin pooling. Such orthopedic casting materials and methods for preparing the same are disclosed and claimed herein.